Modelling and experiments of straw combustion in a grate furnace

A two-dimensional mathematical model for the combustion of straw in a cross -current, moving bed was developed as part of a tool for optimizing operati ng conditions and design parameters. To verify the model and to increase th e understanding of straw bed combustion, laboratory fixed-bed experiments w ere performed in a 15 cm diameter and 137 cm long vertical reactor. Air was introduced through the bottom plate and the straw was ignited from the top with an electrical radiation source. The temperature was measured at eight positions within the bed and gas analysis was performed for O-2, CO2, CO, CxHy, NOx, NH3 and SO2. The inlet air flow rate and air preheat temperature were varied. The experimental data for ignition front temperatures and fro nt propagation velocity compared reasonably well with the modelling results . A higher air inlet temperature resulted in lower maximum bed temperatures , which was successfully modelled. A limited parameter analysis study was p erformed. Measurement of NO from the bed showed that, within the air inlet flow rates investigated, the conversion of fuel nitrogen to NO decreased wi th increasing air flow rate during ignition front propagation, while the co nversion increased during the char burnout phase. (C) 2000 Elsevier Science Ltd. All rights reserved.